Modern methods of soft tissue reconstruction call for the simultaneous use of materials that frequently have several incompatible properties. For example, in treating ventral hernia through the intra-peritoneal on-lay mesh method (laparoscopic IPOM), the synthetic implant material should ensure anti-adhesion on the visceral side (facing the internal organs). On the parietal side (facing the abdominal wall) it is desirable to ensure the tissue's controllable integration into the implant. The growing tissues should not shrink or crimple the implant in the distant post-operation period. At the same time, the tissue integration should reliably secure it to the abdominal wall tissue.
The porous structure of the implant surface should also meet criteria. For instance, macrophage cells and neutrophils, killers of bacteria, are unable to penetrate fine pores measuring less than 10 μm. This enables the bacteria, smaller than 1 μm, to form colonies in pores measuring less than 10 μm and in spaces of multi-filament meshes, which causes a risk of infection. Therefore it is desirable for the implant to have a structure in which the pores and gaps in the mesh plexus nodes would not be below 75 μm. See C N Brown, J G Finch “Which mesh for hernia repair?”, Ann R Coll Surg Engl. 2010 May, available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3025220/. It is desirable that the synthetic implant should have a minimum tissue response and be strong and elastic enough for clinical applications. It is desirable that the implant should be able to be sutured or fastened with a surgical stapler. The strength of the implant should be commensurable to the stress sustained by the abdominal wall during coughing, jumping, etc. (e.g., tensile strength up to 32 N/cm). At the same time, the implant should feature elasticity close to that of the abdominal wall (e.g., up to 38% at the maximum stress).
The task of creating such an implant has not been fulfilled since the implants known to date do not provide all of the desired capabilities.
Currently available implants contain layers of different non-absorbable materials fastened together by some means. In most cases, the layer that ensures integration of the abdominal wall tissues is a polypropylene or polyester mesh whilst the layer that provides the anti-adhesive barrier is made from polytetrafluoroethylene or, for instance, collagen. Such designs are described in the following patents and publications: U.S. Pat. No. 6,258,124 titled “Prosthetic repair fabric”, U.S. Pat. No. 6,652,595 titled “Method of repairing inguinal hernias”, U.S. Pat. No. 5,743,917 titled “Prosthesis for the repair of soft tissue defects”, U.S. Patent Publication No. 20020052654 titled “Prosthetic repair fabric”, U.S. Pat. No. 8,206,632 titled “Method of making composite prosthetic devices having improved bond strength”, and U.S. Pat. No. 8,623,096 titled “Double layer surgical prosthesis to repair soft tissue,” the entirety of each is hereby incorporated by reference.
Implants are available that are essentially in the form of a mesh from a stable strong material (polypropylene, polyester or other) coated with a temporary absorbable anti-adhesive material. The mesh is designed for soft tissues to grow into it whilst the absorbable layer, separating the mesh from visceral tissues, creates a temporary anti-adhesive barrier promoting the formation of peritoneum and minimizing the probability of union with the mesh during the wound healing. Following the biological degradation of the barrier, the mesh integrates into the abdominal wall tissue.
Such designs are described in the following publications: U.S. Patent Publication No. 20130317527 titled “Single plane tissue repair patch having a locating structure”, U.S. Patent Publication No. 20130267971 titled “Single plane tissue repair patch”, and U.S. Patent Publication No. 20130267970 titled “Single plane tissue repair patch,” the entirety of each is hereby incorporated by reference. An example of commercial use of such a design is an implant under the trade name of PHYSIOMESH manufactured by ETHICON, Inc.
All these implants feature strength that ensures a high restorative effect and are fit for suture-aided fixation, but are disadvantageous in some aspects.
By virtue of its micro-porous structure, polytetrafluoroethylene mollifies the gravity and reduces the commissural side effects of the healing process, but does not altogether eliminate them. The use of collagen implies a high risk of a tissue rejection, allergic response or infection.
Another disadvantage is the shrinkage of the implant, which is specific to materials known to date (polypropylene, polyester). Growing through the mesh, the organism tissues contribute to its extra shrinkage and wrinkling, which negatively impacts the quality of the patient's life.
It is not recommended to introduce implants coated with a temporary absorbable anti-adhesive material in the event of a casual or scheduled opening of the digestive tract lumen or in the event of infection of the site since this may result in the infection of the implant itself, as its absorbable material promotes colonization of microorganisms, which may trigger a post-operative pyoinflammatory process.
These implants have either a mesh-like or porous structure, which ensures integration of the abdominal wall tissues, but makes it impossible to control the size of the mesh pore and cell. The material structure is usually determined by the range of pore and cell size. In woven materials the mesh weave areas are inaccessible during sterilization and are potentially a place of microbial contamination and a site of bacterial infection.
All these factors may restrict the use of implants in various clinical cases.